The present invention relates to a signal processing circuit, a method of processing a signal, an audio signal processing circuit, an imaging apparatus, a method of processing an audio signal with an imaging apparatus, a recording apparatus, a method of recording, a playing apparatus, and a method of playing, all capable of reducing periodic noise having a variable period and/or noise level.
An imaging apparatus, such as a portable video camera, generates various noises while capturing an image. An example of a noise generated inside the imaging apparatus is a periodic noise generated at a predetermined period at a frequency of about 150 Hz caused by, for example, the rotation of a rotary drum in case where the recording medium is a magnetic tape.
When a microphone included in the imaging apparatus picks up sound and records the sound on a recording medium, in addition to the target sound, noise generated inside the imaging apparatus is picked up, reducing the quality of the recorded sound. Japanese Unexamined Patent Application Publication No. 11-176113 describes a technology for reducing periodic noise by using a synchronous adaptive filter that is configured to adaptively change the filter coefficient in response to the periodic noise.